1. Field of the Invention
The present invention relates to locking electrical connectors, especially for power cords using the standard two-prong or three-prong arrangement with two straight blade prongs and a round prong for the ground connection on the plug, with a mechanisms or means to prevent the plug from being pulled out of the socket.
2. Description of the Prior Art
A common problem with power tools is that the power is interrupted by the extension cord being pulled out. The prongs of a conventional power plug are held by the female receptacle, or socket, with friction alone. This friction cannot be too great, lest the connection be too difficult to make and disassemble by hand; but the limited friction force cannot hold against ordinary forces on an extension cord which are encountered in the workplace, or elsewhere that electrical appliances are moved or that cords may be pulled on.
Because of the weight of an extension cord, and the friction of the cord""s insulation, there is much greater force on the appliance end of an extension cord, or chain of cords, than at the wall socket end. Separation usually occurs at the female end of an extension cord.
Raymond Altergott et al, in U.S. Pat. No. 5,286,213, discloses an extension cord with a socket (female connector) that mates with a standard or conventional male power plug and attempts to secure the male plug, by gripping the prongs of the male plug inside the socket. The gripping is actuated by a cylindrical external sleeve on the socket; rotating the sleeve moves an internal cam mechanism and causes the two terminal blades of the plug to be grasped tightly by internal metal pieces. The tight grip of the metal pieces on the two prongs makes electrical contact and mechanically grasps the prongs to resist pull-out of the plug.
A provisional patent application of Raymond A. Altergott and Thomas P. Masbaum, dated Jul. 21, 1995 and entitled xe2x80x9cLocking Electrical Outletxe2x80x9d, illustrates in one of the drawing sheets a device very similar to FIG. 1 of the Altergott et al. ""213 patent, but without any external cylindrical sleeve. The relative motion is supplied by rotation of an inner socket portion relative to the housing; rather than grasping the housing and the sleeve and rotating them, the housing and plug are grasped and rotated.
An alternate embodiment of Altergott uses the same mechanism as is disclosed in the ""213 patent, mounted in a connection box instead of at the end of a power cord.
The Altergott device has several drawbacks. First, the retention force is limited to that of friction; there is no actual locking, because the plug can be pulled by sliding of one surface over another; no part needs to be moved aside, no ledge or step need be overcome, to separate the plug and socket. Second, all separating and bending forces are taken by the prongs, which are not always strongly seated in the body of the plug; the very forces which the device is intended to resist can damage the plug by loosening, bending, or even pulling out the prongs. It would be better if at least part of the force were to be taken by the thick plastic body of the plug, but it is not. Third, the mechanism is complex and, if made to the standards of many electrical fittings, will fail prematurely. The Altergott device is non-repairable.
Haag, in U.S. Pat. Nos. 5,722,847 and 5,344,333, discloses a system of joining power cords which overcomes one drawback of the Altergott device, namely the reliance on prong friction to prevent separation. Haag joins the plug and socket by screw threads. The threads are set on a xe2x80x9cface platexe2x80x9d which interacts with a rotatable cylindrical sleeve, that couples housings of the plug (male portion) to the socket (female portion). Haag uses two conical housings with internal parts held in place within by screws inserted through the housing wall in a direction parallel to the axis of the cone. Cylindrical portions extend from the bases of the conical portions, and those cylindrical portions are covered the cylindrical sleeve.
Haag""s male and female connectors are custom made. If a regular plug were mated to the female connector, there would be no resistance to separation beyond that of any plug and socket. The Haag patents do not disclose an extension cord that will mate with a conventional male power plug and securely lock to it. Because a special plug is needed for secure locking, there will always be a xe2x80x9cweak linkxe2x80x9d in any chain of power connections. For example, if a user wishes to hook up a hand saw, there will be no more than the usual resistance to pull-out even if the sockets and all extension cords have Haag""s custom socket/plug structures, because the drill saw itself will have a conventional plug that can pull out.
The provisional application of Raymond A. Altergott and Thomas P. Masbaum that was mentioned above discloses an extension cord female end and plug each having a cylindrical portion. These two portions align when the connection is made, and form a single cylinder. A cylindrical sleeve, with two pairs of offset lugs protruding from its inner surface, is slidable over the single cylinder. It appears in the drawing that the sleeve locks the socket and plug together with grooves in the surfaces of the cylinders and lugs on the inside of the sleeve, which slide in the grooves, moving between locked and unlocked positions as the lugs slide from one position to another in the grooves.
The male plug of the provisional application is specially made, with the cylindrical portion, and the grooves required for locking, being molded directly into the body of the plug. Like the Haag device, the Altergott/Masbaum device cannot lock the conventional plug of a conventional extension cord, hand drill, etc.
Sweatman et al., in U.S. Pat. No. 5,755,588, discloses a xe2x80x9cretention enclosurexe2x80x9d which is usable with a conventional plug/socket combination. After the connection is made, the socket and plug are encased inside the enclosure, which includes an upper half and a lower half. The enclosure holds the socket, the plug, and their respective cords merely with friction; there is no positive latch or locking mechanism to prevent the plug from being pulled out.
Sweatman""s FIG. 2 shows that the enclosure is long enough that, when the friction grip on the cords is overcome by a force pulling the connection apart, the plug and socket can be pulled into the ends of the enclosure to break the connection. One of Sweatman""s objects is accommodate connections xe2x80x9chaving a variety of sizes and shapesxe2x80x9d, and thus the shorter connections cannot possible be held securely.
Moreover, the closure mechanism is not only weak (a snap-clasp opposite a live hinge) but it is also located in the center of the enclosure, so that the two halves can be easily sprung apart at either end of the enclosure. This weakness is related to the multiple functions of the housing: it must securely hold, but still be releasable.
Because the Sweatman housing closes over both socket and plug, it must be removed to separate the plug from the socket. Thus, if a worker wishes to change a saw for a drill, for example, he or she must remove the housing entirely, change the appliance plug, and then reassemble the housing over the joined connection. This is awkward and time-consuming, and sooner or later the enclosure will be lost between plug insertions.
The Sweatman device cannot be used with a wall socket because there is no cord attached to the female portion of a wall socket. It can only be used to join one extension cord to another extension cord.
Elswick, in U.S. Pat. No. 5,584,720, discloses a cord plug lock that has an internal compartment just long enough to accommodate the joined pair of socket and plug. At either end is a slot through which the cord can move to the center line, so that the joined socket and plug are held inside. Elswick""s device, like Sweatman""s, can be lost during plug changes. Elswick illustrates its device with sockets and plugs having rounded ends, which present a definite surface against which the internal end surfaces of Elswick""s lock can bear. The more usual plug design has a strain relief, lacks a definite end surface, and could not be made secure by the Elswick device.
The prior art does not disclose a socket or extension cord adapted to accept and securely hold in place a conventional male plug, such as the male plug of a power tool, which permits quick plug changes for various different appliances, which attaches plugs securely without relying on friction forces alone, and which has no loose parts to be lost during plug changes.
One object of the invention is adapt any conventional power plug to be securely held and quickly exchanged with another plug in a socket, whether the socket is at the end of an extension cord, in a wall, coupled to an appliance, or elsewhere.
Another object is to provide a plug adapter which can be used with conventional sockets and extension cords.
A further object is a plug locking system with no loose parts.
A still further object is to provide a plug connector which can be removed from the plug.
The present invention provides a plug adapter and two means for securing the plug adapter, which are denoted as the lock and the connector. The lock, which should be quickly and easily released, secures the plug adapter to the socket; the second means secures the plug adapter to a conventional plug, and may be semi-permanent or even permanent. The adapter has special features for locking to the socket of the present invention, but it also can be used with a conventional socket such as a common wall outlet or the female end of a conventional extension cord. That is why the connection of the adapter to the plug can be semi-permanent, or permanent; there is no reason to take it off.
The adapter, by separating the two functions of securing and releasing the plug, makes it possible for each function to be done in a better manner.
The preferred lock is actuated by a sliding cylindrical sleeve which is not removable from the socket. It cannot be lost.
With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.